This invention relates to a movable base jack. More particularly, this invention relates to a movable base jack in which the lift member is connected to a wheel assembly which rolls in a guideway attached to the jack pad. The movable base jack of this invention has particular utility as a positioning and levelling jack for supporting shelter units in a level position regardless of the terrain.
Various portable hand-operated machines for lifting heavy weights or otherwise exerting great force by utilizing the principle of the lever, screw, toggle joint or hydraulic press are well known in the prior art. Also known in the art are levelling jacks with movable bases for positioning the jack directly below the load, such as a shelter unit, to be lifted. By utilizing a movable base on the jack, the lift member of the jack and the object to be lifted can be maintained in a perpendicular relation. In this manner, purely vertical forces are exerted on the weight such that the jack is operating at maximum efficiency and the load to be lifted, such as a shelter unit, is maintained level.
However, many of these prior art devices can only move in one planar direction. Also, many of these devices are inefficient due to the high friction losses experienced in moving the jack within its base. An example of this latter type device can be seen in commonly-owned U.S. Pat. No. 3,604,166 in which the sliding jack is subject to high friction loading due to sand or dirt entrapped within the slide trough. Further, the jack mounting is subject to high moment loads.